Crossover manifold



Feb. 13, 1951 c. H. WIEGMAN 2,541,973

' CROSSOVER MANIFOLD Filed June 25, 1948 2 Sheets-Sheet 1 (la/ Myra INVENTOR;

I BYM C. H. WIEGMAN CROSSOVER MANIFOLD Feb. -12., 1951 2 Sheets-Sheet 2 Filed June 25, 1948 2 0;. 33m mzGzw 4O FUEL FLOW- LB HR we INVENTOR.

BY Zzm I Patented Feb. 13, 1951 CROSSOVER MANIFOLD Clarence'H. Wiegman, Williamsport, Pa., assignor to Avco Manufacturing Corporation, Cincinnati, Ohio, a corporation of Delaware Application June 25, 1948, Serial No. 35,133

2 Claims.

This invention relates to exhaust systems for internal combustion engines.

The system is particularly well adapted for use on opposed multi-cylinder aircraft engines. In engines of this general type, it has heretofore been the practice to exhaust the combustion gases into a manifold for discharge to the atmosphere, either directly through short conduits or stacks or through longer conduits opening into remote portions of the slip stream.

A conventional type of exhaust manifold usually carries, in the same conduit, exhaust from two or more consecutively firing cylinders. Thus, in opposed cylinder engines, it is customary to carry off the exhaust gas from each bank of cylinders in a single conduit. These individual conduits may either be joined together in a single manifold or extended independently into a muffler or some convenient portion of the slip stream. In a manifold, however, the exhaust impulses overlap, thereby building up back pressure in the exhaust system and appreciably reducing the developed engine horsepower.

When the manifold is connected into a muffler, further interference or constriction occurs which, in turn, produces a further diminution in engine horsepower. Therefore, since it is extremely desirable, especially in aircraft engines, to maintain a high operating efficiency, the problem of reducing exhaust noises without impairing such efiiciency is extremely difiicult of solution.

It is accordingly an object of this invention to provide an exhaust system for internal combustion engines effective to maintain an extremely low back pressure against which the engine cylinders operate in discharging the products of combustion.

Another object of the invention is the provision of an exhaust system for internal combustion engines specially adapted for use with a muffler so as to reduce exhaust noise without decreasing developed engine horsepower.

A salient feature of the applicants invention is the manner in which the exhaust system functions so as to accomplish the above objects and simultaneously therewith actually increase engine horsepower over that which would be developed with the engine discharging directly to the atmosphere through short stacks.

Other objects and features of the invention will become evident from a consideration of the detailed discussion composed with reference to the accompanying drawings.

Broadly the invention comprehends the provision of a crossover manifolding system espemagnetos 8 and 9.

cially adapted for use on a four cylinder opposed type of internal combustion engine. It contemplates a crossover adapted to provide a discharge channel for each pair of alternately firing cylinders, thereby providing for an exhaust impulse in each channel every 360 of crankshaft rotation rather than at intervals of -540-180-540 as is customary with conventional manifolds. This enables the pressurized charge of exhaust gas to expand and move through the muffler before the next charge is exhausted into the discharge channel.

In this way, there is no overlapping of impulses so as to cause choking in the manifold or channel. Thus, not only is back pressure on the engine cylinders avoided but forces of eduction are actually produced in the discharge channels tending to draw off the ensuing charge of exhaust gas. It is therefore evident that the applicants exhaust system will effectively reduce the engine noise level while actually increasing appreciably the developed or crankshaft horsepower.

In the accompanying drawings which constitute a part of this application:

Fig. 1 is a bottom view of a four cylinder opposed type engine equipped with an exhaust system embodying the invention.

Fig. 2 is a side elevation view of the engine and exhaust system shown in Fig .1.

Fig. 3 is a view illustrating one manner in which exhaust conduits may be joined to provide a common discharge line.

Fig. 4 is a chart comparing engine speed and fuel consumption for an engine having short exhaust stacks and an engine equipped with the applicant's exhaust system.

Referring to Fig. 1 of the drawings, I, 2, 3 and 4 designate cylinders of a standard opposed type aircraft engine including a conventional crankcase 5, propeller shaft 6, propeller hub I and twin Cylinders I and 2 are provided with exhaust ports I I and [2, respectively, connected to discharge into a common header or manifold l5 terminating at 21a, in a muffler 20 having an outlet 22. I Exhaust ports I3 and it are provided on cylinders 3 and 4, respectively, and connected into a common header or manifold 15 terminating at 21b in the muffler 20. The muffler 20, of suitable size and construction, may be conveniently located beneath either the engine or the fuselage of an aircraft not here shown.

In fabricating the separate manifolds l5 and I6, short lengths of conduits such as IE1) are blended and welded into longer conduits adapted for connection at one end of the muffler. The other end of these long conduits are adapted, as at la, for attachment to the remaining cylinder in each group.

This completes a description of the structural details of the invention; however, to facilitate a more thorough comprehension of the invention, a discussion is now directed to the manner in which the invention performs its intended function.

In operation, the engine cylinders I, 2, 3 and 4 are assigned a firing order of l, 3, 2, 4 dictated by the selected crankshaft design. Therefore, as the engine is of the 4 cycle type having four exhaust strokes every 720 of crankshaft rotation, consecutive firing cylinders will exhaust every 180, or half turn. Consequently, if non-consecutive or alternate firing cylinders |-2 and 3 and 4 are manifolded together, an exhaust impulse is released in each of the common headers l5 and [6 every 360. By allowing a complete turn of the crankshaft to separate each exhaust impulse, the burned gases have an opportunity to expand and pass through the exhaust system.

In this way there is no overlapping of exhaust impulses in the manifold and accordingly interfer'ence and choking in the exhaust system is avoided. Such operation reduces back pressure on the cylinders thereby increasing the developed crankshaft horsepower. Experimental results have further shown that if manifolding similar to that illustrated in Fig. 3 is employed, eduction currents are set up within the manifold which reduce the effective back pressure on the individual cylinders below that which would obtain it short stacks were used dischargin directly to the atmosphere.

The resultant effect of such operation is best illustrated by reference to the chart comprising Fig. 4. Curve A is the performance curve for an engine equipped with the applicants exhaust system and curve B indicates the performance of an engine exhausting directly to the atmosphere through short stacks.

By selecting an operating speed of 2600 R. P. M. and a corresponding fuel consumption rate of fifty-two (52) pounds per hour, it is seen that the engine speed varies by approximately 85 R. P. M. This represents an increase in speed of approximately 3.3%. However, as the gain in horsepower is also partially dependent upon the effective pressure within the cylinder, this figure does not represent the actual gain in developed crankshaft power. Test results have shown this increase in horsepower to be approximately 10%, which represents a substantial gain without any increase in fuel consumption or any appreciable increase in weight.

It is apparent, therefore, that the applicants invention would have special significance for the aircraft industry where smaller ratios of weight and fuel consumption per developed horsepower are constantly being sought so as to reduce the over-all plane weight and simultaneously therewith increase the cruising range and performance characteristics of the craft.

While this invention has been described with reference to the details of a single embodiment, it will be appreciated by those skilled in the art that the principles involved are susceptible of numerous other applications.

What I claim, therefore, and wish to secure by Letters Patent is:

1. An exhaust system for a four cylinder, four cycle opposed-type internal combustion engine each of the cylinders of which has an exhaust port through which combustion products are vented periodically, said exhaust system comprising a pair of exhaust pipes, each of said pipes being connected to the exhaust ports of a pair of alternately firing cylinders, a muffler having spaced openings, an exhaust pipe bein connected to each of the muffler openings, each of said exhaust pipes comprising a first pipe extending between the exhaust port of one of the associated cylinders and said muffler, and a second pipe joining the exhaust port of the other associated cylinder and an intermediate portion of the first named pipe, said second named pipe terminating at the wall of said first named pipe, whereby dynamic pressure surges established between the cylinders and said muflier by the venting of combustion products produce low pressure regions adjacent the cylinder exhaust ports at the time of venting of combustion products.

2. In a four cylinder, four cycle opposed-type internal combustion engine having banked pairs of cylinders extending radially outwardly perpendicular to the engine crankshaft at opposite sides thereof, a first exhaust manifold extending laterally entirely across said engine in a direction generally parallel to the cylinders in one bank, said exhaust manifold communicating with each of said cylinders in said bank, a second exhaust manifold extending laterally across said engine in a direction generally parallel to the cylinders in said other bank, said second exhaust manifold communicating with each of said cylinders in said other bank, and a muffler having spaced openings at its opposite sides for attachment of said exhaust manifolds, each of said exhaust manifolds comprising a continuous length of pipe communicating at one end with a cylinder and at the other end with an opening of said muffler, and a second pipe communicating at one end with the other cylinder and terminating at its opposite end at the wall of said first named pipe, bein attached thereto for communication with its interior.

CLARENCE H. WIEGMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,094,431 Frederickson Apr. 28, 1914 FOREIGN PATENTS Number Country Date 440,955 Great Britain Jan. 9, 1936 697,940 France Nov. 5, 1930. 

